There are currently over a million concrete ties in track of the railroads in North America using Pandrol-type fastening systems. Such systems typically comprise an embedded Pandrol-like shoulder, Pandrol-type fastener clips and various types of pads and insulators. Typically, the Pandrol-like shoulders are ductal iron elements which are embedded about 51/2 inches (14 cm) into the body of the concrete tie and protrude about 11/2 inches (4 cm) above the surface of the tie to define a 0.938 inch (2.38 cm) diameter cylindrical bore which is parallel to the axis of the rail. This shoulder further defines a ledge on the side of the bore opposite the rail which is about 0.865 inches (2.19 cm) above the rail surface, and is adapted to receive a rail clip as described hereinafter. Rails are installed between the iron shoulders by first placing molded plastic rail pads between the shoulders, which pads are approximately 71/2 inches (19 cm) long and about 73/4 inches (19.7 cm) wide, having two 9/16 inch (1.4 cm) cut-outs on either side which are about 3 1/16 inches (8 cm) in length. These cut-outs permit the pads to be fitted between opposing shoulders. These pads are typically 0.2 inches .+-.0.02 inches, or about 3/16 inch (4.76 mm), thick and for the most part are extremely stiff, being made typically of ethylene vinyl acetate copolymer resin such as Dupont grade EVA 3130.
Once these pads are in place a rail is put into position between the shoulders. Rail insulators are then placed adjacent to the shoulders and over and against adjacent surfaces of the rail base. Typically these insulators are about 0.394 inches (1 cm) thick, and comprise bosses which extend for a short distance along the side faces of their adjacent shoulders to maintain their position. Anchoring of the rail is accomplished using a rail clip which is typically a short length of 7/8 inch (2.2 cm) heat treated steel rod which has been formed so that each of the ends thereof are parallel and spaced apart from each other. One of these ends is forced into the cylindrical bore of the iron shoulder, while the other seats against the aforementioned ledge formed on that shoulder. The portion of the clip disposed between these two ends is configured so that it contacts the top surface of the rail insulator and presses the rail insulator, rail base, and rail pad against the concrete tie.
While the aforementioned system has experienced considerable commercial success in this country, it has been found that severe cracking of the concrete ties due to high impact coupling between the rail and the concrete tie often results, particularly when the road bed is used for high speed travel. This high impact coupling is caused by wheel and/or rail surface irregularities, and is aggravated by deterioration of insulators and pads in service. Although it would appear that the provision of thicker pads might remedy the problem, the geometry of the rail shoulder and Pandrol-like fastener practically insures that alternate or substitute thicknesses cannot be use. Further due to the combination of torque and bending stresses inherent in the configuration of the clip, deflection of the clip in service produces an eccentric bending moment. This torque hysteresis causes the clip to be sensitive to small rail/wheel anomalies and work out of the shoulder.
Deterioration of concrete ties has been found to be particularly severe in the vicinity of insulated rail joints. At insulated rail joints, a head bond block of plastic impregnated paper is disposed between two adjacent rail ends. This head block interrupts the monolithic nature of the rail and causes a different flexure than is normally encountered in continuous rail. The head bond block also causes a surface anomaly between the rails, since the ends of these rails are slightly spaced apart by the head bond block. The sides of adjacent rail ends located at an insulated joint are typically fitted with bonded joint bars which are wrapped with insulation, and therefore are not in electrical contact with the rails. These bonded joint bars are normally bonded and bolted to both sides of the rails using epoxies and heavy duty nuts and bolts which are insulated from the rail using full length insulating bushings.
In present Pandrol-type systems, "J" clips (with insulating caps) are used to hold down rails in the vicinity of the rail joints, including insulated rail joints. Unfortunately, the configuration of these "J" clips is such that they cannot be made to bear on the bonded joint bar if a joint bar bolt is located adjacent to the Pandol-like shoulder. Accordingly, it may be necessary to omit certain hold down clips in the vicinity of certain rail joints. Deterioration of concrete ties in the vicinity of such rail joints is accordingly accelerated due to the lack of a hold down system which is completely effective in the rail joint region, particularly in regions of insulated rail joints.